The hippocampus is part of the limbic system that directs various bodily functions. Limbic system is located in the medial temporal lobe near the center of the brain. There is one part of the hippocampus on each side of the head.

The hippocampus is seahorse-shaped and is about 1/100th of the size of the cerebral cortex (the brain’s outer layer). It has three layers made of pyramidal cells.

Functions of the hippocampus

The hippocampus’ main function involves human learning and memory.

In terms of memory, the hippocampus helps us process and retrieve 2 specific types of long-term memories:

Explicit memory. This type of memory consists of facts and events that can be consciously and purposely declared. For example: An actor learns to memorize speeches or lines in a play.

Spatial relationships. This type of memory help us specify location of objects and their relation with other reference objects. For example: The taxi drivers remember routes through a city.

The hippocampus is not responsible for procedural memory (a part of the long-term memory that deal with how to perform certain procedures, such as walking, talking or riding a bike) and short-term memory. These types of memory are handled by the cortex and the cerebellum.

What happens if the hippocampus gets damaged?

There would be serious problems happening to the memory whether both of the hippocampi are removed or just one one hippocampus is damaged.

In particular, when the hippocampus experience imparment, the patients can no longer develop new long-term memories. They can remember things happened long time ago just fine but fail to remember some things that recently happened before the hippocampal damage. For example, an affected individual is able to draw a map of the neighborhood he lived in as a small child, but have difficulty going to a store in a new area. Other times, he may have trouble getting from one place to another.

Diseases that affect the hippocampus

Transient global amnesia (TGA)

This is a condition in which memory loss develops in all of a sudden then goes away quickly (temporary memory loss). Researchers still do not know what causes this incident and they believe it possibly because of damage to the hippocampus. Most of the times, patients with TGA eventually regain their memories.

Alzheimer’s disease and depression

Some diseases actually change the physical form of the hippocampus, for example Alzheimer’s disease and depression. These two illnesses result in smaller hippocampus.

The change in Alzheimer’s disease’s case is so obvious that doctors monitor the volume of the hippocampus to see how the disease progresses.

With depression, the impact is just as significant. Researchers have found that suffering from depression, a person’s hippocampus can waste away and shrink. The lost volume can be up to 20%. nevertheless, scientists are still studying to see which one came first: a smaller hippocampus or depression.

Epilepsy

The link between the hippocampus and epilepsy is really strong when the hippocampus the place where a lot of epileptic seizures begin.

50% to 75% of patients with epilepsy appeared to have damage to their hippocampus when undergoing autopsies. However, it is not clear if the epilepsy results in the hippocampus damage.